I really do hope they switch to Hindu numbers rather than Roman at some point if they go that far. It's going to be awfully weird if we ever get to a Final Fantasy L. I actually had to look up what 50 was in Roman numbers, so I doubt I'm the only one that wouldn't immediately recognise FFL as FF50
I doubt they can get back to 3 mainline titles a gen, but 2 should definitely be possible. Especially if they use different teams for each of them, and don't have any screw-ups that require shifting all of their resources to something else *cough* FF14 *cough*
You're missing Final Fantasy XXX, which would be totally awesome, but still. I want to think they'll drop the Roman numerals once they reach the XXs, but who knows.